The Langmuir-Blodgett technique of the like is a well-known method of preparing a crystal or film as in "A new technique for investigating lipid protein films" by Peter Fromherz (Biochim. Biophys. Acta 225 (1971) 382-387. This technique was originally developed to prepare a two-dimensional film or crystal from a surfactant that is insoluble in water. In recent years, as an extended application of this technique a method of preparing crystals or films from molecules of materials other than surfactants has been proposed. According to this proposed method, a surfactant is spread over the surface of water in which such molecules are dissolved that will form a crystal or film. The dissolved molecules are attracted to the surfactant, and finally they orientate themselves together with the surfactant at the surface of water to form a two-dimensional crystal or film.
The crystal or film prepared by the aforementioned method contains the surfactant, as well as the desired molecules. Therefore, it is impossible to prepare a pure crystal or film by the method. Further, molecules capable of forming crystals or the like are restricted to those molecules attracting surfactants and so it is not possible to form crystals or the like from molecules not attracting surfactants. In addition, molecules that can act on surfactants are limited to those molecules which exist only near the surface of water and limited in amount, although the desired molecules are previously dissolved in water. Most of the molecules remain dissolved in water, making the efficiency of utilization of the molecules very low.